U.S. patent application number 09/925211 was filed with the patent office on 2002-04-18 for polyimide film, method of manufacture , and metal interconnect board with polyimide film substrate.
Invention is credited to Sawasaki, Kouichi, Uhara, Kenji, Yasuda, Naofumi.
Application Number | 20020045033 09/925211 |
Document ID | / |
Family ID | 18742520 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020045033 |
Kind Code |
A1 |
Uhara, Kenji ; et
al. |
April 18, 2002 |
Polyimide film, method of manufacture , and metal interconnect
board with Polyimide film substrate
Abstract
A polyimide film is produced by copolymerizing pyromellitic
dianhydride in combination with phenylenediamine,
methylenedianiline and 3,4'-oxydianiline in a specific molar ratio.
The polyimide film, when used as a metal interconnect board
substrate in flexible circuits, chip scale packages (CSP), ball
grid arrays (BGA) or tape-automated bonding (TAB) tape by providing
metal interconnects on the surface thereof, achieves a good balance
between a high elastic modulus, a low thermal expansion
coefficient, alkali etchability and film formability.
Inventors: |
Uhara, Kenji; (Nagoya,
JP) ; Yasuda, Naofumi; (Tokai, JP) ; Sawasaki,
Kouichi; (Nagoya, JP) |
Correspondence
Address: |
E I DU PONT DE NEMOURS AND COMPANY
LEGAL DEPARTMENT - PATENTS
1007 MARKET STREET
WILMINGTON
DE
19898
US
|
Family ID: |
18742520 |
Appl. No.: |
09/925211 |
Filed: |
August 9, 2001 |
Current U.S.
Class: |
428/195.1 ;
428/209 |
Current CPC
Class: |
C08J 2379/08 20130101;
H05K 1/0346 20130101; Y10T 428/24917 20150115; C08J 5/18 20130101;
Y10T 428/24802 20150115; C08G 73/1042 20130101; Y10T 428/31721
20150401 |
Class at
Publication: |
428/195 ;
428/209 |
International
Class: |
B32B 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 24, 2000 |
JP |
2000-253421 |
Claims
What is claimed is:
1. A polyimide film made from a polyamic acid prepared from a
tetracarboxylic dianhydride comprising pyromellitic dianhydride in
combination with phenylenediamine, methylenedianiline and
3,4'-oxydianiline such as to satisfy conditions (1-a) to (1-c)
below:10 mol %.ltoreq.X.ltoreq.60 mol % (1-a)20 mol
%.ltoreq.Y.ltoreq.80 mol % (1-b)10 mol %.ltoreq.Z.ltoreq.70 mol %
(1-c)wherein X is the mole percent of phenylenediamine, Y is the
mole percent of methylenedianiline, and Z is the mole percent of
3,4'-oxydianiline, each based on the total amount of diamine, and
further wherein the tetracarboxylic dianhydride and total diamine
are in a molar ratio of about 0.9 to 1.1.
2. The polyimide film of claim 1 which is made from a polyamic acid
selected from a block component-containing polyamic acid and an
interpenetrating polymer network component-containing polyamic
acid.
3. The polyimide film of claim 1 or 2, wherein the phenylenediamine
is p-phenylenediamine.
4. A method of manufacturing a polyimide film, the method
comprising the steps of, in order: (A) reacting starting materials
comprising (a1) a tetracarboxylic acid dianhydride comprising
pyromellitic dianhydride and (a2) a first diamine selected from
phenylenediamine, methylenedianiline and 3,4'-oxydianiline, in an
inert solvent to form a first polyamic acid containing a component
selected from a block component of the first diamine and
pyromellitic dianhydride and an interpenetrating polymer network
component of the first diamine and pyromellitic dianhydride; (B)
adding to the first polyamic acid prepared in step A additional
materials comprising (b1) a tetracarboxylic acid dianhydride
comprising pyromellitic dianhydride and (b2) a second diamine and a
third diamine selected from phenylenediamine, methylenedianiline
and 3,4'-oxydianiline, and continuing the reaction with all the
materials; (C) mixing into the second polyamic acid solution
obtained in step B a chemical agent capable of converting the
polyamic acid into polyimide; (D) casting or extruding the mixture
from step C onto a smooth surface to form a polyamic acid-polyimide
gel film; and (E) heating the gel film at 200 to 500.degree. C. to
transform the polyamic acid to polyimide; wherein at least one of
the first diamine, second diamine and third diamine is a
phenylenediamine; at least one of the first diamine, second diamine
and third diamine is a methylenedianiline; and at least one of the
first diamine, second diamine and third diamine is
3,4'-oxydianiline.
5. The method of claim 4, wherein conditions (1-a) to (1-c) below
are satisfied:10 mol %.ltoreq.X.ltoreq.60 mol % (1-a)20 mol
%.ltoreq.Y.ltoreq.80 mol % (1-b)10 mol %.ltoreq.Z.ltoreq.70 mol %
(1-c);wherein X is the mole percent of phenylenediamine, Y is the
mole percent of methylenedianiline, and Z is the mole percent of
3,4'-oxydianiline, each based on the total amount of diamine, and
further wherein the tetracarboxylic dianhydride and total diamine
are in a molar ratio of about 0.9 to 1.1.
6. The method of claim 5, wherein conditions (2-a) to (2-c) below
are satisfied:20 mol %.ltoreq.X.ltoreq.50 mol % (2-b)30 mol
%.ltoreq.Y.ltoreq.70 mol % (2-c)10 mol %.ltoreq.Z.ltoreq.50 mol %
(2-d)wherein the tetracarboxylic dianhydride and total diamine are
in a molar ratio of about 0.98 to 1.02.
7. A metal interconnect board for use in flexible printed circuits
or tape-automated bonding tape, which board is produced by using
the polyimide film of claim 1 as the substrate and providing metal
interconnects on the surface thereof.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polyimide film which has
a high elastic modulus, a low thermal expansion coefficient, alkali
etchability and excellent film-forming properties when used as a
metal interconnect board substrate on the surface of which metal
interconnects are provided to form a flexible printed circuit or
tape-automated bonding (TAB) tape. The invention relates also to a
method for manufacturing such film. The invention additionally
relates to a metal interconnect board for use in flexible printed
circuits or TAB tape in which the foregoing polyimide film serves
as the substrate.
[0003] 2. Description of the Related Art
[0004] TAB tape is constructed of a heat-resistant film substrate
on the surface of which are provided very fine metal interconnects.
In addition, the substrate has openings, or "windows," for mounting
integrated circuit (IC) chips. Sprocket holes for precisely feeding
the TAB tape are provided near both edges of the tape.
[0005] IC chips are embedded in the windows on the TAB tape and
bonded to the metal interconnects on the tape surface, following
which the mounted chip-bearing TAB tape is bonded to a printed
circuit for wiring electronic equipment. TAB tape is used in this
way to automate and simplify the process of mounting IC chips on an
electronic circuit, and also to improve manufacturing productivity
and enhance the electrical characteristics of electronic equipment
containing mounted IC chips.
[0006] TAB tapes currently in use have either a three-layer
construction composed of a heat-resistant substrate film on the
surface of which an electrically conductive metal foil has been
laminated with an intervening layer of polyester, acrylic, epoxy or
polyimide-based adhesive, or a two-layer construction composed of a
heat-resistant substrate film on the surface of which a conductive
metal layer has been directly laminated without an intervening
layer of adhesive.
[0007] The substrate film in TAB tape is thus required to be heat
resistant. Polyimide film in particular has been used to ensure
that the substrate film is able to withstand high-temperature
operations such as soldering when IC chips are bonded to the metal
interconnects on TAB tape and when the IC chip-bearing TAB tape is
bonded to a printed circuit for wiring electronic equipment.
[0008] However, the heat incurred in the process of laminating
polyimide film with metal foil or a metal layer then chemically
etching the metal foil or metal layer to form metal interconnects
may elicit differing degrees of dimensional change in the polyimide
film and metal, sometimes causing considerable deformation of the
TAB tape. Such deformation can greatly hinder or even render
impossible subsequent operations in which IC chips are mounted on
the tape and the IC chip-bearing TAB tape is bonded to a printed
circuit for wiring electronic equipment. Accordingly, a need has
been felt for some way to make the thermal expansion coefficient of
polyimide film closer to that of the metal so as to reduce
deformation of the TAB tape.
[0009] Moreover, reducing dimensional change due to tensile and
compressive forces in TAB tape on which IC chips have been mounted
and which has been bonded to a printed circuit for wiring
electronic equipment is important for achieving finer-pitch metal
interconnects, reducing strain on the metal interconnects and
reducing strain on the mounted IC chips. To achieve this end, the
polyimide film used as the substrate must have a higher elastic
modulus.
[0010] According to the definition of a polymer alloy or blend (see
"Polymer Alloys: New Prospects and Practical Applications," in High
Added Value of Polymer Series, edited by M. Akiyama and J. Izawa,
published in Japan by CMC K.K., April 1997), block, blend,
interpenetrating polymer network (IPN) and graft polymerization all
fall within the category of processes capable of increasing the
elastic modulus of a polymer.
[0011] With respect to polyimides in particular, Mita et al. (J.
Polym. Sci. Part C: Polym. Lett 26, No. 5, 215-223) suggest that,
on account of the molecular composite effect, a blend of different
polyimides can more readily attain a high elastic modulus than a
copolyimide obtained from the same starting materials. However,
because polyimide molecules have large molecular cohesive forces,
mere blends of such molecules tend to take on a phase-separated
structure. Some form of physical bonding is needed to inhibit such
phase separation.
[0012] An interpenetrating network polymer was proposed for this
very purpose by Yui et al. ("Functional Supermolecules: Their
Design of and Future Prospects," in New Materials Series, edited by
N. Ogata, M. Terano and N. Yui, published in Japan by CMC K.K.,
June 1998).
[0013] A specific example of a blend according to the prior-art is
disclosed in JP-A 63-175025, which relates to polyamic acid
compositions (C) made up of a polyamic acid (A) of pyromellitic
acid and 4,4'-diaminodiphenyl ether and a polyamic acid (B) of
pyromellitic acid and phenylenediamine. JP-A 63-175025 also
discloses polyimides prepared from such polyamic acid compositions
(C).
[0014] However, the methods provided in this prior art involve
first polymerizing the different polyamic acids, then blending them
together. Because thorough physical interlocking of the type seen
in an interpenetrating network polymer cannot be achieved in this
way, phase separation may occur during imidization of the polyamic
acid. In some cases, a slightly hazy polyimide film is all that can
be obtained.
[0015] JP-A 1-131241, JP-A 1-131242, U.S. Pat. No. 5,081,229 and
JP-A 3-46292 disclose block copolyimide films manufactured from
block copolyamic acids composed of pyromellitic dianhydride,
p-phenylenediamine, and 4,4'-diaminodiphenyl ether. This prior art
also discloses methods for manufacturing copolyamic acid films
composed of block components of ultimately equimolar composition by
reacting non-equal parts of the diamines and the acid dianhydride
in an intermediate step.
[0016] However, in such prior-art processes, although the polyamic
acid blend solution prepared is not prone to phase separation, the
molecular composite effect is inadequate and a satisfactory
increase in rigidity is not always achieved. Moreover, because
polymer production involves copolymerization using block components
in which the molecular chains are regulated, the reaction steps are
complex and reaction takes a longer time. Also, the reaction passes
through a step in which there exists an excess of reactive end
groups, which tends to destabilize the polyamic acid in the course
of production, making it subject to changes in viscosity and
gelation. In addition to these and other production problems, the
above prior-art methods sometimes fail to provide a film having a
sufficiently high Young's modulus.
[0017] The surface of the polyimide film substrate is sometimes
roughened by etching with an alkali solution prior to use so as to
improve the adhesive strength of an adhesive applied thereto.
Alkali etching is also at times used to form through holes or vias
for interconnects. Accordingly, there has arisen a desire for
polyimide films having excellent alkali etchability.
[0018] A film having good planarity is desirable for better ease of
handling in processing operations. The planarity of the film can be
improved by increasing the stretch ratio during film production.
Hence, film compositions capable of being subjected to orientation
at a high stretch ratio are also desired.
[0019] Methods for producing polyimide films which satisfy such
requirements have already been proposed. For example, JP-A
1-131241, JP-A 1-131242 and JP-A 3-46292 provide polyimide films
made from polyamic acid prepared from pyromellitic dianhydride,
p-phenylenediamine, and 4,4'-diaminodiphenyl ether. The same prior
art also teaches processes for producing block component-containing
polyamic acid film by reacting non-equal parts of diamine and acid
dianhydride in an intermediate step.
[0020] However, the above-described prior art methods provide
polyimide films which have properties when used as a substrate for
metal interconnect boards, which need to be improved.
[0021] It is therefore an object of the invention to provide a
polyimide film which has a high elastic modulus, a low thermal
expansion coefficient, alkali etchability and excellent film
formability when used as a metal interconnect board substrate of a
type that can be provided on the surface with metal interconnects
to form a flexible printed circuit, chip scale packages, ball grid
arrays or TAB tape. Another object of the invention is to provide a
method of manufacturing such a film. A further object of the
invention is to provide a metal interconnect board in which the
foregoing polyimide film serves as the substrate.
SUMMARY OF THE INVENTION
[0022] The present invention is directed to a polyimide film made
from a polyamic acid prepared from a tetracarboxylic dianhydride
comprising pyromellitic dianhydride in combination with
phenylenediamine, methylenedianiline and 3,4'-oxydianiline such as
to satisfy conditions (1-a) to (1-c) below:
10 mol %.ltoreq.X.ltoreq.60 mol % (1-a)
20 mol %.ltoreq.Y.ltoreq.80 mol % (1-b)
10 mol %.ltoreq.Z.ltoreq.70 mol % (1-c);
[0023] wherein X is the mole percent of phenylenediamine, Y is the
mole percent of methylenedianiline, and Z is the mole percent of
3,4'-oxydianiline, each based on the total amount of diamine, and
further wherein the tetracarboxylic dianhydride and total diamine
are in a molar ratio of about 0.9 to 1.1 [0022]
[0024] In another embodiment, the present invention is directed to
a method of manufacturing a polyimide film comprising the steps of,
in order:
[0025] (A) reacting starting materials comprising (a1) a
tetracarboxylic acid dianhydride comprising pyromellitic
dianhydride and (a2) a first diamine selected from
phenylenediamine, methylenedianiline and 3,4'-oxydianiline, in an
inert solvent to form a first polyamic acid solution containing a
block component or interpenetrating polymer network component of
the first diamine and pyromellitic dianhydride;
[0026] (B) adding to the first polyamic acid solution prepared in
step A additional materials comprising (b1) a tetracarboxylic acid
dianhydride comprising pyromellitic dianhydride and (b2) a second
diamine and a third diamine selected from phenylenediamine,
methylenedianiline and 3,4'-oxydianiline, and continuing the
reaction with all the materials to form a second polyamic acid
solution;
[0027] (C) mixing into the second polyamic acid solution obtained
in step B a chemical agent capable of converting the polyamic acid
into polyimide;
[0028] (D) casting or extruding the mixture from step C onto a
smooth surface to form a polyamic acid-polyimide gel film.
[0029] (E) heating the gel film at 200 to 500.degree. C. to
transform the polyamic acid to polyimide wherein at least one of
the first diamine, second diamine and third diamine is a
phenylenediamine; at least one of the first diamine, second diamine
and third diamine is a methylenedianiline; and at least one of the
first diamine, second diamine and third diamine is
3,4'-oxydianiline.
[0030] In another embodiment, the invention is directed to a metal
interconnect board for flexible printed circuits or TAB tape, which
board is produced by using any of the above-described polyimide
films of the invention as the substrate and providing metal
interconnects on the surface thereof.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The polyimide making up the inventive film may be a block
copolymer, a random copolymer or an IPN polymer.
[0032] Preferred block components or IPN polymer components are
polyamic acids composed of phenylenediamine and pyromellitic
dianhydride, and polyamic acids composed of 3,4'-oxydianiline and
pyromellitic dianhydride. After forming a polyamic acid containing
such block components or IPN polymer components, the polyamic acid
is imidized to give a block component or IPN polymer
component-containing polyimide.
[0033] The polyamic acid-forming reaction is divided and carried
out in at least two stages. First, a block component or an IPN
polymer component-containing polyamic acid is formed. In a second
step, this polyamic acid is reacted with additional diamine and
dianhydride to form additional polyamic acid. The polyimide polymer
is formed by imidization after the second step.
[0034] The polyimide polymer of the present invention can be used
to form a polyimide film having a good balance of properties
suitable for use as the substrate in metal interconnect boards for
flexible printed circuits, chip scale packages, ball grid arrays
and TAB tapes; namely, a high elastic modulus, a low thermal
expansion coefficient, alkali etchability, and film
formability.
[0035] By additionally incorporating in the polyimide polymer a
block component or an IPN polymer component, the various above
properties can be brought within even more preferable ranges. The
block component or IPN polymer component used for this purpose is
most preferably one prepared by the reaction of phenylenediamine
with pyromellitic dianhydride.
[0036] The diamines used in the invention are linear or rigid
diamines such as phenylenediamine, semi-rigid diamines such as
3,4'-oxydianiline, and flexible diamines such as
methylenedianiline.
[0037] The phenylenediamine used in the invention may be
p-phenylenediamine, m-phenylenediamine, o-phenylenediamine, or a
partially substituted phenylenediamine. The use of
p-phenylenediamine is especially preferred. In the practice of the
invention, p-phenylenediamine serves to increase the elastic
modulus of the film. At an amount of p-phenylenediamine less than
10 mol %, based on the total amount of diamine, the film obtained
lacks sufficient stiffness, whereas an amount of p-phenylenediamine
greater than 60 mol % results in too low a film elongation.
Preferably, the p-phenylenediamine is present in an amount of from
20 to 50 mol %.
[0038] Methylenedianiline is produced in relatively large
quantities, and so is an aromatic diamine that is inexpensive and
easy to acquire. It has the effect of imparting flexibility to the
film. A methylenedianiline content below 20 mol %, based on the
total amount of diamine, leads to an excessive increase in the unit
cost of the film, whereas a methylenedianiline content greater than
80 mol % results in poor film elongation. Preferably, the
methylenedianiline is present in an amount of from 30 to 70 mol
%.
[0039] In the invention, 3,4'-oxydianiline increases film
elongation and improves film formability. At less than 10 mol % of
3,4'-oxydianiline, based on the total amount of diamine, film
elongation is inadequate. On the other hand, a 3,4'-oxydianiline
content greater than 70 mole % lowers the glass transition
temperature, resulting in a poor heat resistance and excessive
thermal shrinkage. Preferably, the 3,4'-oxydianiline is present in
an amount of from 10 to 50 mol %.
[0040] The tetracarboxylic dianhydride used in the invention is
pyromellitic dianhydride, although concomitant use may be made of
other tetracarboxylic dianhydrides within a range in the amount of
addition that does not compromise the objects of the invention. For
example, less than 50 mol % of biphenyltetracarboxylic dianhydride
or benzophenonetetracarboxylic dianhydride may be used.
[0041] The resulting polyamic acid is converted to the polyimide by
imidization.
[0042] The elastic modulus of the polyimide film can be adjusted by
varying the proportion of phenylenediamine and 3,4'-oxydianiline in
the diamine used to prepare the polyamic acid. Increasing the
amount of p-phenylenediamine improves the elastic modulus and
dimensional stability, but also has the undesirable effect of
increasing moisture uptake. Increasing the methylenedianiline
reduces film elongation, and may result in poor film formability.
It is thus necessary to adjust the molar ratio of the respective
constituents with great care in order to achieve a good balance in
the various properties.
[0043] The polyimide film of the invention can be manufactured by a
combination of conventional methods for making polyimide, although
a preferred method of production for easily achieving the inventive
polyimide film comprises the steps of, in order:
[0044] (A) reacting starting materials comprising (al) a
tetracarboxylic acid dianhydride comprising pyromellitic
dianhydride and (a2) a first diamine selected from
phenylenediamine, methylenedianiline and 3,4'-oxydianiline, in an
inert solvent to form a first polyamic acid solution containing a
block component or interpenetrating polymer network component of
the first diamine and pyromellitic dianhydride;
[0045] (B) adding to the first polyamic acid solution prepared in
step A additional materials comprising (b1) a tetracarboxylic acid
dianhydride comprising pyromellitic dianhydride and (b2) a second
diamine and a third diamine selected from phenylenediamine,
methylenedianiline and 3,4'-oxydianiline, and continuing the
reaction with all the materials to form a second polyamic acid
solution;
[0046] (C) mixing into the second polyamic acid solution obtained
in step B a chemical agent capable of converting the polyamic acid
into polyimide;
[0047] (D) casting or extruding the mixture from step C onto a
smooth surface to form a polyamic acid-polyimide gel film.
[0048] (E) heating the gel film at 200 to 500.degree. C. to
transform the polyamic acid to polyimide.
[0049] In the method of manufacturing polyimide film of the
invention, conditions (1-a) to (1-c) for the polyamic acid are
preferably limited respectively to conditions (2-a) to (2-c)
below:
20 mol %.ltoreq.X.ltoreq.50 mol % (2-a)
30 mol %.ltoreq.Y.ltoreq.70 mol % (2-b)
10 mol %.ltoreq.Z.ltoreq.50 mol % (2-c).
[0050] It is also preferable in the inventive method for the
phenylenediamine to be p-phenylenediamine. The inventive method,
when subjected to the above conditions, is able to achieve even
better effects.
[0051] The polyamic acid of the invention is generally prepared at
a temperature of not more than 175.degree. C., and preferably not
more than 90.degree. C., by reacting the above-described
tetracarboxylic dianhydride and diamine in a molar ratio of about
0.90 to 1.10, preferably 0.95 to 1.05, and most preferably 0.98 to
1.02, within an organic solvent that is non-reactive for each of
these constituents.
[0052] Each of the above constituents may be added independently
and successively or simultaneously to an organic solvent.
Alternatively, a mixture of the constituents may be added to an
organic solvent. However, to carry out a uniform reaction, it is
advantageous to add each constituent successively to the organic
solvent.
[0053] If successive addition is carried out, the order in which
the constituents are added is preferably one in which precedence is
given to the diamine and tetracarboxylic dianhydride constituents
used to prepare the block component or IPN polymer component. That
is, the reaction involved in the production of a polyamic acid
containing a block component or an IPN polymer component is divided
into at least two stages. First, a block component or IPN polymer
component-containing polyamic acid is formed. In a second step,
this polyamic acid is reacted with additional diamine and
dianhydride to form additional polyamic acid. The polyimide polymer
is formed by imidization after the second step.
[0054] The time required to form the block component or IPN polymer
component may be selected based on the reaction temperature and the
proportion of block component or IPN polymer component within the
polyamic acid, although experience shows that a time within a range
of about 1 minute to about 20 hours is suitable.
[0055] As discussed later in the specification, to form a block
component-containing polymer, it is preferable for the diamine and
the tetracarboxylic dianhydride in reaction step (A) to be
substantially non-equimolar. To form an IPN polymer component, it
is preferable for the diamine and the tetracarboxylic dianhydride
in the reaction step to be substantially equimolar or, in cases
where the reaction passes through a reaction step in which excess
diamine is present, for the ends to be capped with a dicarboxylic
anhydride. The reason for having the diamine and the
tetracarboxylic dianhydride substantially equimolar or, in a
reaction step involving the presence of excess diamine, for having
the ends capped with a dicarboxylic anhydride is to make the first
polymer component formed in these reaction steps chemically inert
so as not to be incorporated onto the ends of the polyimide polymer
formed in the subsequent reaction step. At the same time, carrying
out the IPN polymer first component-forming reaction and the
subsequent polyimide-forming reaction in the same reactor
facilitates the formation of molecular composites (composites
between different molecules), makihg it possible to better manifest
the distinctive features of the first IPN polymer component.
[0056] A specific example is described below of the preparation of
a polyimide containing a block component or an IPN polymer
component composed of pyromellitic dianhydride and
p-phenylenediamine by using pyromellitic dianhydride as the
tetracarboxylic dianhydride and by using p-phenylenediamine,
methylenedianiline and 3,4'-oxydianiline as the diamines.
[0057] First, p-phenylenediamine is dissolved in dimethylacetamide
as the organic solvent, then pyromellitic dianhydride is added and
the block component or IPN polymer component reaction is carried
out to completion.
[0058] Methylenedianiline and 3,4'-oxydianiline are then dissolved
in the solution, following which pyromellitic dianhydride is added
and the reaction is effected, giving a four-ingredient polyamic
acid solution containing a block component or IPN polymer component
of p-phenylenediamine and pyromellitic dianhydride.
[0059] It is possible in this case to control the size of the block
component or IPN polymer component by adding a trace amount of
3,4'-oxydianiline and/or methylendianiline to the
p-phenylenediamine initially added or by having the
p-phenylenediamine and pyromellitic dianhydride initially reacted
be non-equimolar and adding an amount of end-capping agent
sufficient to fully react with the excess diamine. However, to take
full advantage of the effects of the block component or IPN polymer
component, it is preferable to prepare an IPN polymer in which the
p-phenylenediamine and the pyromellitic dianhydride are
substantially equimolar.
[0060] The end-capping agent, typically a dicarboxylic anhydride or
a silylating agent, is preferably added within a range of 0.001 to
2%, based on the solids content (polymer concentration). Preferred
examples of dicarboxylic anhydrides include acetic anhydride and
phthalic anhydride. Preferred examples of silylating agents include
non-halogenated hexamethyldisilazane,
N,O-(bistrimethylsilyl)acetamide and
N,N-bis(trimethylsilyl)urea.
[0061] The end point of polyamic acid production is determined by
the polyamic acid concentration in the solution and by the solution
viscosity. Addition at the end of the process of a portion of the
reactants as a solution in the organic solvent used in the reaction
is effective for precisely determining the solution viscosity at
the end point, although adjustment is required to keep the polyamic
acid concentration from falling too low.
[0062] The polyamic acid concentration within the solution is from
5 to 40 wt %, and preferably from 10 to 30 wt %.
[0063] The organic solvent is preferably selected from organic
solvents which do not react with the various reactants or the
polyamic acid obtained as the polymer product, which can dissolve
at least one and perhaps all of the reactants, and which dissolve
the polyamic acid.
[0064] Preferred examples of the organic solvent include
N,N-dimethylacetamide, N, N-diethylacetamide,
N,N-dimethylformamide, N,N-diethylformamide and
N-methyl-2-pyrrolidone. Any one or mixture thereof may be used. In
some cases, concomitant use may be made of a poor solvent such as
benzene.
[0065] During manufacture of the inventive polyimide film, the
polyamic acid solution thus prepared is pressurized with an
extruder or a gear pump and delivered to the polyamic acid film
producing step.
[0066] The polyamic acid solution is passed through a filter to
remove any foreign matter, solids and high-viscosity impurities
which may be present in the starting materials or which may have
formed in the polymerization step. The filtered solution is then
passed through a film-forming die or a coating head, extruded in
the form of a film onto the surface of a rotating or laterally
moving support, and heated from the support to give a polyamic
acid-polyimide gel film in which some of the polyamic acid has
imidized. The gel film is self-supporting. When the film reaches a
peelable state, it is peeled from the support and introduced into
an oven, where it is heated and the solvent is removed by drying to
complete imidization, thereby giving the final polyimide film.
[0067] The use here of a sintered metal fiber filter having a
cutoff of 20 .mu.m is advantageous for excluding gel products that
have formed during the process. A sintered metal fiber filter
having a cutoff of 10 .mu.m is preferred, and a sintered metal
fiber filter with a cutoff of 1 .mu.m is especially preferred.
[0068] Imidization of the interpenetrating polyamic acid may be
carried out by a thermal conversion process in which heating alone
is used, or by a chemical conversion process wherein polyamic acid
containing an imidizing agent is heat treated or the polyamic acid
is immersed in an imidizing agent bath. In the practice of the
invention, if the polyimide film is to be used in a metal
interconnect circuit substrate for flexible printed circuits, chip
scale packages, ball grid arrays or TAB tape, chemical conversion
is preferable to thermal conversion for achieving at the same time
a high elastic modulus, a low thermal expansion coefficient, alkali
etchability, and film formability.
[0069] Moreover, a manufacturing process in which an imidizing
agent is mixed into the polyamic acid and the solution is formed
into a film then heat-treated to effect chemical conversion offers
numerous advantages, including a short imidization time, uniform
imidization, easy peeling of the film from the support, and the
ability to handle in a closed system imidizing agents which have a
strong odor and must be isolated. Accordingly, the use of this type
of process is preferable to a process in which the polyamic acid
film is immersed in a bath of the imidizing agent and the
dehydrating agent.
[0070] A tertiary amine which promotes imidization and a
dehydrating agent which absorbs the water that forms in imidization
are used together as the imidizing agent in the invention.
Typically, the tertiary amine is added to and mixed with the
polyamic acid in an amount that is substantially equimolar to or in
a slight [stoichiometric] excess relative to the amount of amic
acid groups in the polymer. The dehydrating agent is added to the
polyamic acid in an amount that is about twice equimolar or in a
slight [stoichiometric] excess relative to the amount of amic acid
groups in the polymer. However, the amounts of addition may be
suitably adjusted to achieve the desired peel point from the
support.
[0071] The imidizing agent may be added at any time from
polymerization of the polyamic acid to when the polyamic acid
solution reaches the film-forming die or coating head. To prevent
imidization from occurring during delivery of the solution, the
imidizing agent is preferably added to the polyamic acid solution
and mixed therewith in a mixer a little before the solution reaches
the film-forming die or coating head.
[0072] The tertiary amine is preferably pyridine or
.beta.-picoline, although use can also be made of other tertiary
amines such as .alpha.-picoline, 4-methylpyridine, isoquinoline or
triethylamine. The amount may be adjusted according to the activity
of the particular tertiary amine used.
[0073] Acetic anhydride is most commonly used as the dehydrating
agent, although use can also be made of other dehydrating agents
such as propionic anhydride, butyric anhydride, benzoic acid
anhydride or formic acid anhydride.
[0074] Imidization of the imidizing agent-containing polyamic acid
film proceeds on the support owing to heat received from both the
support and the space on the opposite side of the film, resulting
in a partially imidized polyamic acid-polyimide gel film which is
then peeled from the support.
[0075] A larger amount of heat received from the support and the
space on the opposite side of the film accelerates imidization and
allows more rapid peeling of the film. However, too much heat
results in the rapid release of organic solvent volatiles between
the support and the gel film, causing undesirable deformation of
the film. A suitable heat quantity should therefore be selected
after due consideration of both the peel point position and
potential film defects.
[0076] The gel film that has been peeled from the support is
carried to an oven, where the solvent is removed by drying and
imidization is completed.
[0077] The gel film contains a large amount of organic solvent, and
thus undergoes a large reduction in volume during drying. To
concentrate dimensional shrinkage from such volumetric reduction in
the direction of film thickness, the gel film is generally held at
both edges with tenter clips and passed through a drying apparatus,
or tenter frame, by the forward movement of the tenter clips.
Inside the tenter frame, the film is heated, thereby integrally
carrying out both drying (removal of the solvent) and
imidization.
[0078] Such drying and imidization are carried out at a temperature
of 200 to 500.degree. C. The drying temperature and the imidization
temperature may be the same or different, although increasing the
temperature in a stepwise manner is preferred. Typically, to
prevent film blistering due to removal of the solvent, a somewhat
low temperature within the above range is used at the stage where a
large amount of solvent is removed by drying. Once the danger of
film blistering has passed, the temperature is ramped up to a
higher level within the above range to accelerate imidization.
[0079] Within the tenter frame, the film can be stretched or
relaxed by increasing or decreasing the distance between the tenter
clips at both edges of the film.
[0080] Preferably, cut sheets of block component or IPN polymer
component-containing polyimide film obtained by using chemical
conversion to effect imidization are cut from a film that has been
continuously manufactured in the manner described above. However, a
small amount of the same type of film can be produced by a process
in which, as described subsequently in the examples, a block
component or IPN polymer component-containing polyamic acid is
prepared within a plastic or glass flask, following which a
chemical conversion agent is mixed into the polyamic acid solution
and the resulting mixture is cast onto a support such as a glass
plate and heated to form a partially imidized self-supporting
polyamic acid-polyimide gel film. The resulting film is peeled from
the support, attached to a metal holding frame or similar apparatus
to prevent dimensional change, and heated, thereby drying the film
(removing the solvent) and effecting imidization.
[0081] Compared with polyimide films obtained by thermal
conversion, polyimide films according to the invention that have
been thus manufactured by using chemical conversion to effect
imidization, when employed as a metal interconnect circuit
substrate in flexible printed circuits, chip scale packages, ball
grid arrays and TAB tape, provide a high elastic modulus, a low
thermal expansion coefficient, a low moisture expansion
coefficient, and a low moisture uptake. Moreover, they have
excellent alkali etchability.
[0082] Therefore, metal interconnect boards for flexible printed
circuits, chip scale packages, ball grid arrays or TAB tape that
are manufactured by using the inventive polyimide film as the
substrate and providing metal interconnects on the surface thereof
exhibit a high performance characterized by an excellent balance of
properties; namely, a high elastic modulus, a low thermal expansion
coefficient, alkali etchability, and excellent film
formability.
[0083] Preferably, the polyimide film of the invention has an
elastic modulus of at least 4 GPa, a thermal expansion coefficient
of 10 to 20 ppm/.degree. C., and a moisture uptake of not more than
2%, and especially not more than 1%. The alkali etchability is
preferably such as to allow dissolution of the film. As described
below, evaluation of the alkali etchability can be carried out
based on the surface etch rate under alkaline conditions.
[0084] In the soldering step, the film is exposed to elevated
temperatures close to 300.degree. C. Hence, it is preferable for
the film to have a low thermal shrinkage. In some cases, use of the
film can be difficult if the thermal shrinkage is greater than 1%.
Hence, a thermal shrinkage of not more than 1%, and especially not
more than 0.1% is preferred.
EXAMPLES
[0085] Examples are given below by way of illustration, although
the examples are not intended to limit the invention. The various
film properties were measured as described below.
[0086] Abbreviations
[0087] DMAc dimethylacetamide
[0088] MDA methylenedianiline
[0089] 34'-ODA 3,4'-oxydianiline, also referred to as
3,4'-diaminodiphenyl ether
[0090] PDA p-phenylenediamirie
[0091] PMDA pyromellitic dianhydride
[0092] Test Procedures
[0093] (1) Elastic Modulus and Elongation at Break
[0094] The elastic modulus was determined in accordance with JIS
K7113 from the slope of the first rise in the tension-strain curve
obtained at a test rate of 300 mm/min using a Tensilon tensile
tester manufactured by Orientech Inc.
[0095] The elongation at break was obtained as the elongation when
the same test specimen broke.
[0096] (2) Thermal Expansion Coefficient
[0097] The temperature of a sample was increased at a rate of
10.degree. C./min then decreased at a rate of 5.degree. C./min
using a TMA-50 thermomechanical analyzer manufactured by Shimadzu
Corporation. The dimensional change in the sample from 50.degree.
C. to 200.degree. C. at the time of the second rise or fall in
temperature was used to determine the thermal expansion
coefficient.
[0098] (3) Moisture Uptake
[0099] A film sample was held for 48 hours in a test chamber
(STPH-101, manufactured by Tabai Espec Corp.) kept at 25.degree. C.
and 95% relative humidity. The moisture uptake was the weight gain
relative to the weight of the sample when dry, expressed as a
percentage of the dry weight.
[0100] (4) Alkali Etchability
[0101] One surface of a polyimide film sample was placed in contact
with a 1 N potassium hydroxide solution in ethanol/water (80/20 by
volume) at 40.degree. C. for 120 minutes, and the film thickness
before and after contact was measured using a Litematic thickness
gauge (supplied by Mitutoyo Corp.). The alkali etchability was
rated as shown below based on the percent change in thickness.
[0102] Good: Change in thickness of at least 5%
[0103] Fair: Change in thickness of at least 1% but less than
5%
[0104] Poor: Change in thickness of less than 1%
[0105] (5) Warping of Metal Laminate
[0106] A polyimide-base adhesive was coated onto the polyimide
film, and copper foil was laminated thereon at a temperature of
250.degree. C. The adhesive was then cured by raising the
temperature to a maximum of 300.degree. C. The resulting metal
laminate was cut to a sample size of 35.times.120 mm. The samples
were held for 24 hours at 25.degree. C. and 60% relative humidity,
following which the extent of warp in each sample was measured.
Measurement consisted of placing the sample on a flat sheet of
glass, and measuring and averaging the height of the four corners.
The extent of warping was rated as indicated below. A "Large"
rating means that use of the sample as a metal interconnect board
would result in handling problems during conveyance in subsequent
operations.
[0107] Small: Less than 1 mm of warp
[0108] Moderate: At least 1 mm but less than 3 mm of warp
[0109] Large: At least 3 mm of warp
[0110] (6) Film Formability
[0111] A prepared film was biaxially oriented at the same speed in
both directions and 400.degree. C. on a polymeric film biaxial
orientation system for laboratory use (BIX-703, manufactured by
Iwamoto Seisakusho Co., Ltd.), and the film surface area at break
was determined. The preheating time was 60 seconds and the one-side
stretch rate was 10 cm/min.
[0112] Excellent: Areal stretch ratio at break is greater than
1.3.
[0113] Good: Areal stretch ratio at break is 1.1 to 1.2.
[0114] Fair: Areal stretch ratio at break is 1 to 1.1. Acceptable
for practical purposes.
[0115] Poor: Areal stretch ratio at break is less than 1. Film
formation is difficult.
[0116] (7) Thermal Shrinkage
[0117] The percent dimensional change before and after heating at
300.degree. C. for 1 hour was measured in accordance with
JIS-C2318.
Percent thermal shrinkage=100.times.(A-B)/A
[0118] where
[0119] A represents the film dimensions before heating
[0120] B represents the film dimensions after heating
[0121] Good: Less than 0.05%
[0122] Fair: At least 0.05% but less than 0.1%
[0123] Poor: More than 0.1%
Example 1
[0124] A 500 cc glass flask was charged with 150 ml of
dimethylacetamide, following which p-phenylenediamine was added to
the dimethylacetamide and dissolved, then methylenedianiline,
3,4'-oxydianiline and pyromellitic dianhydride were successively
added. The flask contents were stirred at room temperature for
about one hour, ultimately giving a solution containing 20 wt % of
a polyamic acid of the composition shown in Table 1 in which the
tetracarboxylic dianhydride and the diamines were about 100 mol %
stoichiometric.
[0125] Next, 30 g of this polyamic acid solution was mixed with
12.7 ml of dimethylacetamide, 3.6 ml of acetic anhydride and 3.6 ml
of .beta.-picoline to form a mixed solution. The resulting solution
was cast onto a glass plate, then heated for about 4 minutes over a
150.degree. C. hot plate, thereby forming a self-supporting
polyamic acid-polyimide gel film. The film was subsequently peeled
from the glass plate.
[0126] The gel film was set in a metal holding frame equipped with
numerous pins and heated for 30 minutes while raising the
temperature from 250.degree. C. to 330.degree. C., then heated for
about 5 minutes at 400.degree. C., giving a polyimide film having a
thickness of about 25 .mu.m.
[0127] The properties of the resulting polyimide film are shown in
Table 1.
Examples 2 to 4
[0128] A 500 cc glass flask was charged with 150 ml of
dimethylacetamide, following which p-phenylenediamine was added to
the dimethylacetamide and dissolved, then pyromellitic dianhydride
was added and the flask contents were stirred at room temperature
for about one hour. Methylenedianiline and 3,4'-oxydianiline were
subsequently fed to the resulting polyamic acid solution and
completely dissolved, following which the flask contents were
stirred at room temperature for about one hour. Next, phthalic
anhydride was added in an amount of 1 mol %, based on the diamines,
and the flask contents were again stirred for about one hour,
giving a solution containing 20 wt % of a polyamic acid of the
composition shown in Table 1 in which the tetracarboxylic
dianhydride and the diamines were about 100 mol %
stoichiometric.
[0129] In each example, this solution having a polyamic acid
concentration of 20 wt % was treated by the same method as in
Example 1, giving polyimide films having a thickness of about 25
.mu.m.
[0130] The properties of the resulting polyimide films are shown in
Table 1.
1TABLE 1 Copolyimide films Thermal Elastic expansion Warping
Percent Constituents (mol %) modulus coefficient Elongation Alkali
of metal Film thermal PMDA PDA MDA 34'-ODA (GPa) (ppm/.degree. C.)
(%) etchability laminate formability shrinkage Example 1 100 40 30
30 4.2 14 70 good small good good Example 2 100 40 50 10 4.1 15 50
good small good good Example 3 100 30 50 20 3.8 20 60 good small
good good Example 4 100 20 70 10 3.5 19 50 good small good fair
Examples 5 to 7
[0131] A 500 cc glass flask was charged with 150 ml of
dimethylacetamide, following which p-phenylenediamine was added to
the dimethylacetamide and dissolved. Pyromellitic dianhydride was
then added and the flask contents were stirred at room temperature
for about one hour. Next, acetic anhydride was added in an amount
of 1 mol %, based on the diamine component, and the flask contents
were again stirred for about one hour. Methylenedianiline and
3,4'-oxydianiline were then added to this polyamic acid solution
and completely dissolved, following which pyromellitic dianhydride
was added and the flask contents were stirred at room temperature
for about one hour, yielding a solution containing 23 wt % of a
polyamic acid of the composition shown in Table 2 in which the
tetracarboxylic dianhydride and the diamines were about 100 mol %
stoichiometric.
[0132] In each example, the polyamic acid solution was treated by
the same method as in Example 1, giving polyimide films having a
thickness of about 50 .mu.m.
[0133] The properties of the resulting polyimide films are shown in
Table 2.
2TABLE 2 IPN polyimide films Thermal Constituents (mol %) Elastic
expansion Warping Percent First polymer (A) Second polymer (B)
modulus coefficient Elongation Alkali of metal Film thermal PMDA
PDA PMDA MDA 34'-ODA (GPa) (ppm/.degree. C.) (%) etchability
laminate formability shrinkage Example 5 40 40 60 30 30 5.2 10 80
good small good good Example 6 40 40 60 50 10 5.1 10 70 good
moderate good good Example 7 30 30 70 50 20 4.6 15 70 good small
good good
Comparative Example 1
[0134] A 500 cc glass flask was charged with 150 ml of
dimethylacetamide, following which methylenedianiline and
3,4'-oxydianiline were added to the dimethylacetamide and
dissolved, then pyromellitic dianhydride was added and dissolved.
The flask contents were stirred at room temperature for about one
hour, giving a solution containing 20 wt % of a polyamic acid of
the composition shown in Table 3 in which the tetracarboxylic
dianhydride and the diamine were about 100 mol %
stoichiometric.
[0135] This polyamic acid solution was treated by the same method
as in Example 1, giving a polyimide film having a thickness of
about 25 .mu.m.
[0136] The properties of the resulting polyimide film are shown in
Table 3.
Comparative Examples 2 to 6
[0137] Following the same general procedure as in Comparative
Example 1, a 500 cc glass flask was charged with 150 ml of
dimethylacetamide, following which the starting materials in the
proportions shown in Table 3 were successively added to the
dimethylacetamide and dissolved. The flask contents were stirred at
room temperature for about one hour, giving a solution containing
20 wt % of a polyamic acid of the composition shown in Table 3 in
which the tetracarboxylic dianhydride and the diamine were about
100 mol % stoichiometric.
[0138] In each example, the polyamic acid solution was treated by
the same method as in Example 1, giving a polyimide film having a
thickness of about 25 .mu.m.
[0139] The properties of the resulting polyimide films are shown in
Table 3.
3 TABLE 3 Thermal Elastic expansion Warping Percent Constituents
(mol %) modulus coefficient Elongation Alkali of metal Film thermal
PMDA PDA MDA 34'-ODA (GPa) (ppm/.degree. C.) (%) etchability
laminate formability shrinkage Comp. Ex. 1 100 0 70 30 2.5 30 50
good large good poor Comp. Ex. 2 100 50 50 0 The film ruptured
during drying. Comp. Ex. 3 100 70 30 7 0 25 good large poor good
Comp. Ex. 4 100 100 The film ruptured during drying. Comp. Ex. 5
100 100 2.3 32 10 good large poor poor Comp. Ex. 6 100 100 4.7 18
100 good small good poor
[0140] As is apparent from the results shown in Tables 1 to 3,
unlike the two-component polyimide films prepared in the
comparative examples, random copolyimide films and block
copolyimide films according to the present invention produced from
pyromellitic dianhydride, p-phenylenediamine and 3,4'-oxydianiline
by a chemical conversion process satisfy all the desired properties
(high elastic modulus, low thermal expansion coefficient, alkali
etchability, good film formability) at once. Such characteristics
make the inventive films highly suitable as metal interconnect
circuit substrates for use in flexible printed circuits, chip scale
packages, ball grid arrays and TAB tape.
[0141] As demonstrated above, compared with polyimide films
produced by a thermal conversion process, polyimide films according
to the invention, when used in metal interconnect circuit
substrates for flexible printed circuits, chip scale packages, ball
grid arrays or TAB tape, exhibit a high elastic modulus, a low
thermal expansion coefficient, alkali etchability and excellent
film formability.
[0142] Therefore, metal interconnect boards for use in flexible
printed circuits, chip scale packages, ball grid arrays or TAB tape
which are produced by using the polyimide film of the invention as
the substrate and providing metal interconnects on the surface
thereof exhibit an excellent performance characterized by a good
balance of properties: high elastic modulus, low thermal expansion
coefficient, low moisture expansion coefficient, low moisture
uptake, and alkali etchability.
* * * * *